etching (development) in lithography
(rus. травление в литографии)
— A step in the photolithographic process that includes the removal of a negative photoresist from non-exposed area or a positive photoresist from exposed areas of a substrate, covered with a thin film of a photoresist.

Description

Photoresist wet etching has high selectivity but is isotropic and occurs in more than one direction to the substrate surface, not only perpendicular but also horizontally, under the resist layer. As a result, the etched image size exceeds the corresponding mask.

The most commonly used practice is reactive ion etching, where the substrate is covered with a mask and exposed to plasma excited by the high-frequency electric field. Radicals and neutral plasma particles are involved in chemical reactions on the surface, forming volatile products, whereas positive plasma ions bombard the surface and knock out atoms from the unprotected areas of the substrate. An appropriate reactive gas needs to be selected for each material to be dry etched. For example, oxygen plasma (CF4 + O2) is used to etch organic resists, a chlorine-containing plasma (CCl4, BCl3, BCl3 + Cl2, BCl3 + CCl4 + O2) is used to etch aluminium, chlorine and fluoride plasma (CCl4 + Cl2 + Ar, ClF3 + Cl2, CHF3, CF4 + H2, C2F6) is used to etch silicon and its compounds. The disadvantage of dry-etching is lower selectivity as compared with liquid etching.

Ion-beam etching is a variation of dry anisotropic etching. In contrast to reactive ion etching, which combines physical and chemical mechanisms, ion-beam etching is controlled only by the physical process of momentum transfer. Ion-beam etching is a universal method, suitable for any material or combination of materials and having the highest etching resolution among all the methods, making it possible to produce elements smaller than 10 nm.